The present invention relates generally to systems and methods for increasing autopilot control authority and, more particularly, relates to systems and methods for increasing autopilot control authority in vehicles having mechanical flight control systems, such as to reduce Controlled Flight into Terrain (CFIT) accidents in aircraft.
An unacceptable number of aircraft crashes occur every year. In fact, this number has, on average, shown no significant sign of diminishing since 1976, in spite of advances in almost every aspect of aircraft technology. For example, most aircraft are now equipped with an inertial reference system (IRS) which allows them to determine their position after any interval from take-off. The IRS provides the components of the velocity and acceleration vectors of the aircraft. It is possible to derive position data from this data; however, the position has an associated degree of uncertainty. The position data from the IRS may be compared with position data provided by other radio navigational means, e.g., from a Global Positioning System (GPS), which relies on satellites and which provides fairly precise position data with respect to latitude and longitude. Newer GPS systems can establish the aircraft position and altitude by triangulation using four or more satellites.
Even with these increasingly sophisticated systems providing position information, aircraft still crash every year. Investigations into the causes of aircraft crash incidents frequently reveal that the aircraft was operating normally when the crash occurred, i.e., the cause of the crash incident could not be attributed to a system fault. In these types of incidents, often referred to as a Controlled Flight into Terrain (CFIT) accidents or events, the cause is given as pilot error. However, although the pilot may have contributed to the event, had the pilot been given sufficient warning that, for whatever reason, the aircraft was in imminent danger of crashing, evasive action could have been taken and ground contact avoided. Thus, alerting systems such as Ground Proximity Warning Systems (GPWS) and Enhanced Ground Proximity Warning Systems (EGPWS) have been developed as partial solutions to this problem.
Generally, the GPWS is a system designed to provide adequate warning of terrain contact, while accounting for such items as crew recognition and reaction times. More particularly, the GPWS provides a look-down capability that takes into account the rise of terrain along with a projection of that terrain into the aircraft""s flight path. In turn, the GPWS combines the projection of the terrain into the flight path with piloting information to thereby provide an aural indication that a dangerous situation is impending. The EGPWS includes all of the features as the GPWS, but the EGPWS also includes a predictive component. This predictive component enables the EGPWS to provide more warning time as compared to the GPWS. In addition, the EGPWS also incorporates the use of a worldwide digital terrain elevation database and a color-coded display of threat terrain.
Whereas systems such as the GPWS and EGPWS are adequate in alerting aircraft crew of impending dangers, such alerting systems cannot reduce CFIT accidents in situations where the aircraft crew cannot heed the warning of the alerting system and maneuver the aircraft to avoid terrain impact, such as when the crew suffer from spatial disorientation or g-induced loss of conscious. Thus, systems such as the automatic ground collision avoidance system (Auto-GCAS), were developed to address such situations. In this regard, extending the technologies of the GPWS and the EGPWS, the Auto-GCAS has the ability to take control of the aircraft and execute a recovery to avoid terrain impact.
In general, the Auto-GCAS provides aircraft crew with an indication of the aircraft""s descent toward terrain and executes an automatic recovery. More particularly, as the Auto-GCAS has been implemented on an F-16 test aircraft, upon system activation, horizontal chevrons ( greater than  less than ) appear at the side of the pilot""s Heads-Up Display (HUD) as the aircraft maneuvers toward the ground or at low altitude. Then, if the Auto-GCAS determines that a collision avoidance maneuver within a defined period of time is required to avoid terrain, the chevrons begin to move toward each other. If the aircraft has not performed the fly-up maneuver by the time the chevrons meet, the Auto-GCAS automatically initiates a collision avoidance maneuver without further awaiting pilot intervention.
In addition to Auto-GCAS, other systems have been proposed that can take control of an aircraft in various situations. One such system, referred to as xe2x80x9crequired navigation procedures,xe2x80x9d has been proposed by the Federal Aviation Administration (FAA) as a navigation and separation system. In this regard, the required navigation procedures system operates by sending navigational information to the aircraft from a ground controller. With the navigational information, then, the aircraft autopilot system can take control of the aircraft to maneuver the aircraft to the commanded location, regardless of pilot inputs to the contrary.
Whereas systems such as the Auto-GCAS and the required navigation procedures system are beneficial in reducing CFIT accidents, such systems are not typically compatible with all types of aircraft. In this regard, the Auto-GCAS and required navigation procedures system are designed for aircraft having full authority fly-by-wire control systems. Thus, such systems are typically not compatible with aircraft having other types of control systems. For example, neither the Auto-GCAS nor the required navigation procedures system is compatible with aircraft, such as the Boeing 767-200 aircraft, that have mechanical control systems.
In light of the foregoing background, embodiments of the present invention provide a system, autopilot supplement assembly and method for increasing autopilot control authority, such as during automatic collision avoidance maneuvers, FAA commanded navigation, or during activation of any other system that requires full control authority. Advantageously, the system, autopilot supplement assembly and method of embodiments of the present invention are capable of increasing autopilot control authority in a vehicle, such as an aircraft, where the vehicle includes a mechanical flight control system. Embodiments of the system, autopilot supplement assembly and method are capable of increasing the autopilot authority by supplementing the force applied by an autopilot system to at least one control surface of the vehicle such that force imparted by an operator of the vehicle cannot override the autopilot system. Advantageously, the amount of supplemental force is based upon the amount of force imparted counter to the autopilot force, such as the force applied by an operator of the vehicle. Therefore, embodiments of the system, autopilot supplement assembly and method are capable of providing the benefits of Auto-GCAS, the required navigation procedures system or any other such systems that require full control authority of vehicles such as aircraft that have mechanical control systems. Additionally, embodiments of the system, autopilot supplement assembly and method are adapted such that, should the autopilot supplement assembly fail, control force can be applied to override the autopilot force to thereby allow an operator to control the vehicle.
According to one aspect of the present invention a system is provided for increasing autopilot control authority in a vehicle. The system includes an autopilot system, at least one control element and an autopilot supplement assembly. The autopilot system is capable of automatically controlling the vehicle by applying a variable autopilot force to at least one control surface of the vehicle. The control element, on the other hand, is capable of controlling the vehicle by applying a variable control force to control surfaces of the vehicle. In this regard, the control force acts on the control surfaces counter to the autopilot force.
The autopilot supplement assembly of the system is connected to the control element and the control surfaces of the vehicle. As such, the autopilot supplement assembly is capable of measuring the control force. From the measured control force, the autopilot supplement assembly is capable of determining a variable supplemental force. Thereafter, the autopilot supplement assembly is capable of applying a supplemental force to the control surfaces, where the supplemental force acts on the control surfaces in concert with the autopilot force and counter to the control force. In this regard, the sum of the supplemental force and the autopilot force equals a total force that is greater than the control force.
The autopilot supplement assembly can comprise at least one transducer, a controller and at least one cable tension servo. The transducers can be mechanically connected to the control element such that the transducers can measure the control force. In turn, the controller, which can be electrically connected to the transducers, can determine the supplemental force based upon the control force measured by the transducers. The cable tension servos can be electrically connected to the controller and mechanically connected to the control cables and, thus, the control surfaces. As such, the cable tension servos can apply the variable supplemental force to the control surfaces.
The system may be configured to provide the supplemental force under one or more predefined conditions. According to one embodiment, the autopilot supplement assembly is capable of applying the supplemental force when the control force is at least a predefined percentage of a maximum autopilot force. For example, the autopilot supplement assembly can be capable of applying the supplemental force when the control force is at least ninety percent of the maximum autopilot force. In another embodiment, the autopilot supplement assembly is capable of applying the supplemental force when the control force is greater than the maximum autopilot force. The vehicle can comprise an aircraft including a full control authority system capable of commanding the aircraft to perform one or more commanded maneuvers. For example, the full control authority system can comprise an automatic ground collision avoidance system (Auto-GCAS) capable of determining that a collision avoidance maneuver within a defined period of time is required to avoid terrain. In such embodiments, the autopilot supplement assembly can apply the supplemental force when the full control authority system initiates a commanded maneuver, such as when the Auto-GCAS determines that a collision avoidance maneuver is required.
An autopilot supplement assembly and method of increasing autopilot control authority are also provided.